With the increasing complexity of the society, more and more people are succumbing to depression or presenting with depressive-like symptoms. The therapeutic regimen in use today is centered around tricyclic antidepressants (e.g. imipramine hydrochloride, desipramine hydrochloride, etc.). However, these drugs exert various side effects on the cardiovascular system, neuropsychological system, blood, liver, etc. and cannot be considered to be therapeutically satisfactory drugs. Accordingly there has been a standing demand for a new therapeutic agent.
Among the antidepressant drugs under development these days are 1) selective serotonin reuptake inhibitors, 2) specific monoamine reuptake inhibitors, and 3) 5-HT.sub.1A receptor partial agonists.
Meanwhile, aniracetam which is a recently launched nootropic drug is expected to have ameliorative effects on emotional disturbances (anxiety, impatience, depressed mood) after brain infarct.
The cholinergic neurons in the central neurons system are deeply involved in learning and memory and reportedly many nootroic drugs have activity to stimulate neuronal system. On the other hand, it is known that anticholinergic drugs have inhibitory actions on both learning and memory.
Though neither the etiology of depression nor the detailed mechanisms of action of antidepressants have been elucidated as yet, many workers negate the idea that stimulation of the cholinergic nervous system elicits antidepressive effect. Rather, drugs having anticholinergic activity are known to produce antidepressant effects in animal experiments (F. Borsini and A. Meli: Psychopharmacology 94, 147-160, 1988).
The pyroglutamide derivatives to be utilized in accordance with the present invention have been investigated extensively by the present inventors as substances capable of remarkably alleviating learning and memory disabilities(Japanese Kokoku Tokkyo Koho Hei 04-55405; Japanese Kokai Tokkyo Koho Sho 62-252762).